1. Field of the Invention
The invention relates to vehicle axle/suspension systems, and in particular to the suspension assemblies of those systems which are useful for heavy-duty vehicles such as trucks and tractor-trailers. More particularly, the invention is directed to a heavy-duty trailing or leading aim axle/suspension system for trucks and tractor-trailers, in which the axle is securely and efficiently connected to the beams by an improved axle sleeve and axle structure at the axle-to-beam connection. The improved axle sleeve and axle structure, together with the manner in which the axle-to-beam connection is made and assembled, eliminates welds on the axle. Elimination of the welds on the axle in turn eliminates stress risers and localized mechanical property changes in the axle caused by such welds, and thereby increases durability of the axle and the axle-to-beam connection.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Air-ride trailing and leading arm spring beam-type axle/suspension systems also are often used in the industry. For the purpose of convenience and clarity, reference herein will be made to beams, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle air-ride axle/suspension systems that utilize rigid-type beams or spring-type beams and also to heavy-duty vehicle mechanical axle/suspension systems. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the vehicle. The beams of the axle/suspension system can either be an overslung/top-mount configuration or an underslung/bottom-mount configuration. For the purposes of convenience and clarity hereinafter, a beam having an overslung/top-mount configuration shall be referred to as an overslung beam with the understanding that such reference is by way of example, and that the present invention applies to both overslung/top-mount configurations and underslung/bottom-mount configurations. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The end of each beam opposite from its pivotal connection end also is connected to a bellows air spring or its equivalent, which in turn is connected to a respective one of the main members. A brake assembly and one or more shock absorbers also are mounted on the axle/suspension system. A height control valve is mounted on the hanger and is also operatively connected to the beam in order to maintain the ride height of the vehicle. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams, which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride and stabilize the vehicle. More particularly, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental affect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react or absorb at least some of the forces.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system.
One type of prior art axle/suspension system and axle-to-beam connection is shown, described and/or claimed in U.S. Pat. No. 5,366,237, and is owned by the assignee of the present invention. This axle/suspension system provides a means for rigidly connecting the axle to the beam through a connection that substantially surrounds the axle, thereby preventing the axle from assuming a cross-sectional configuration substantially different from its manufactured unaltered cross-sectional configuration due to torsional forces. In one embodiment of the invention shown, described and/or claimed in the '237 patent, the means for rigidly connecting the axle to the beam includes an orifice formed in each of the beam sidewalls. Each orifice substantially surrounds both the axle, which extends through the orifices, and a sleeve that substantially surrounds and is rigidly attached to the axle. The sleeve in turn is rigidly attached to the beam through the orifices in the beam. The sleeve includes a pair of windows into which a continuous weld is laid in order to rigidly attach the sleeve to the axle. These windows are typically located on the front and rear portions of the axle. A weld is laid circumferentially around the axle between the sleeve and each beam sidewall at the sidewall orifice in order to rigidly attach the axle to the beam. An S-cam bearing and a brake chamber of a brake actuation mechanism are attached to the beam.
The welding of the axle sleeve directly to the axle, at the sleeve windows, can potentially create significant stress risers and local mechanical property changes in the axle, as is generally well known in the art. These stress risers and local mechanical property changes in the axle can in turn potentially reduce the life expectancy of the axle.
In response to the considerations created by welding the sleeve directly to the axle, in certain prior art applications axle wall thickness has been increased or other axle-to-beam connection variants have been created without welds where the beam is clamped to the axle via mechanical fasteners, such as U-bolts. However, these mechanically fastened axle-to-beam connection variants are often heavier than the welded variants and often require re-torque of the mechanical fasteners. In addition, increasing axle wall thickness also can undesirably increase weight.
The axle-to-beam connection of the present invention overcomes the aforementioned considerations associated with axle/suspension systems that utilize prior art axle-to-beam connections by eliminating welds on the axle and thereby producing a mechanical lock at the axle-to-beam connection of the axle/suspension system. The elimination of the welds on the axle at the sleeve windows eliminates both stress risers and local mechanical property changes in the axle caused by the welds, thereby improving the life and durability of the axle-to-beam connection.